In dry ice blasting, enabling the selection and dynamically maintaining a gas/dry ice ratio which is selected and is within an allowable range of ratios, and forbidding the selection of a ratio outside of the allowable range.
The art of dry ice blasting involves the impact on a surface to be cleaned by a blasting stream consisting of particles of dry ice in a gas carrier stream. Important parameters include the size (mass) of the particles and the ratio of the masses of gas and the dry ice (xe2x80x9cgas/dry ice ratioxe2x80x9d herein).
Recently-improved apparatus for supplying dry ice particles have presented the opportunity more precisely to match the size of particles and their rate of supply to various flow rates of the gas in varieties of blast cleaning applications. However, those advantages can be lost if the operator is unaware of what is actually occurring in the apparatus, or if he has selected some ratio which is inappropriate to the intended application.
For example, it is possible that an operator to reduce operating costs, would choose a ratio so heavily favoring the gas that there would be insufficient particles to do the job, and that too many of them might be reduced in mass by sublimation. Even more troubling would be his selection of a ratio too heavily favoring the dry ice particles such that the nozzle would plug up and the process stopped. Furthermore excessive dry ice mass could tend to harm delicate objects.
An obvious solution to this problem is simply to train the operator better. This is frequently unworkable because of employee reassignments, and the sporadic use of this equipment.
Another seemingly obvious solution is to limit the operating ranges narrowly and provide many configurations. This leads to confusion and increased equipment expense.
Charts and diagrams are similarly useless because the operator may not understand them, or may choose incorrectly. Perhaps he would not even use them.
Accordingly, it is an object of this invention to provide a system and method based on mass flow of the gas, which will automatically limit selection of gas/dry ice ratios to only an allowable range for a given application, and prevent selection or operation outside of the range. Operation of such a system requires no more basic input than the selection of a gas flow rate respective to a selected gas pressure. Experience and instruction will teach what pressure is desirable for a given task.
This in itself can establish a range of acceptable gas/dry ice ratios. Depending on the nature of the cleaning work to be done, the system may select the ratio, or the operator may select an exact ratio, but only in the permitted range.
This arrangement also makes available the association of specific nozzles in establishing allowable ranges and ratios.
Its is therefore an object of this invention to simplify and authenticate the choice and maintenance of gas/dry ice ratios in a blasting stream.
Apparatus for dry ice blasting conventionally includes a particle source which supplies dry ice particles of selected size and mass at a regulated rate, a source of pressurized gas such as an air compressor when air is used as the carrier gas, a hose receiving the mixed gas and dry ice, and a nozzle for discharging the blasting stream toward a surface to be cleaned.
A major parameter in dry ice blasting is the pressure of the stream. The operator is expected to select an appropriate pressure. The gas flow rate at this pressure is sensed either directly or indirectly. Under control of an adjustable regulator, it will pass the gas from the supply at the selected flow rate.
In one embodiment of the invention, the flow rate is directly measured by a conventional flow meter. In another embodiment it is indirectly determined by measuring the pressure, and with knowledge of the properties of the nozzle orifice, deducing the flow rate. In both embodiments, the control is by a responsive regulator which will pass gas at a selected rate at a given pressure.
The ratio of the combined stream is established by the rate of supply of the dry ice. The dry ice supply is from a particle source which will be operated at a rate to produce the necessary amount of particles to make the correct ratio in the established flow of gas. Accordingly, the regulator control over the particle source is slaved to the gas flow regulator, so the correct ratio will be maintained.
According to this invention, the intended pressure is first selected. Then the airflow rate will be learned or known. Logic within the system establishes a range of gas/ice dry ice ranges that is acceptable. Then the control will establish a ratio, or the operator can select other ratios, but only within the operating range established by the control.
Thereafter, the master/slave relationship of the two regulators will dynamically maintain the supply of dry ice to provide a stream with the correct ratio.
The flow rate may also be deduced from pressure and identity of the nozzle. Nozzles can be physically configured or color coded to indicate their properties as related to measurement of flow at a given pressure.